Advanced Configuration and Power Interface (ACPI) is a specification that makes hardware status information available to an operating system in computers, including laptops, desktop, servers, etc. More information about ACPI may be found in the 500 page “Advanced Configuration and Power Interface Specification,” Revision 2.0a, Mar. 31, 2002, cooperatively defined by Compaq Computer Corporation, Intel Corporation, Microsoft Corporation, Phoenix Technologies Ltd., and Toshiba Corporation. The ACPI specification was developed to establish industry common interfaces enabling robust operating system (OS)-directed motherboard device configuration and power management of both devices and entire systems. ACPI is the key element in operating system-directed configuration and power management (OSPM).
ACPI is used in personal computers (PCs) running a variety of operating systems, such as Windows™, available from Microsoft® Corporation, Linux, available as open source form a variety of vendors, and HP-UX, available from Hewlett-Packard Company. The ACPI also allows hardware resources to be manipulated. For example, ACPI assists in power management by allowing a computer system's peripherals to be powered on and off for improved power management. ACPI also allows the computer system to be turned on and off by external devices. For example, the touch of a mouse or the press of a key may wake up the computer system using ACPI.
Traditionally ACPI has been difficult to work with for a variety of reasons. First, ACPI is not written in the native assembly language of any computer system platform. Instead, ACPI has its own source and machine languages, i.e., ACPI Source Language (ASL) and ACPI Machine Language (AML), respectively. Because of its highly specialized use, there are relatively few ASL programmers. Furthermore, ASL has relatively few constructs because of its limited use. Furthermore, ACPI code is conventionally monolithic in its design. Consequently, this makes it difficult to port the ACPI code to other platforms or even to different configurations of the same platform. Thus, new ASL code needs to be written to work with newly engineered platforms. The limited number of ASL programmers makes writing new code all the more problematic and costly.
ACPI is composed of both static and interpretable tables. At boot-up time, the system firmware (typically the BIOS, or Basic Input/Output System) constructs the static tables, which are consumed by the operating system. The interpretable tables are composed of AML, which is compiled and then merged into the system firmware. The operating system reads the AML from the interpretable tables and executes the architected interfaces, using an ACPI interpreter. In this fashion, the operating system manipulates hardware resources. Because the interpretable tables are merged into the system firmware, this conventional method lacks flexibility, and scalability, and requires considerable time to re-program to accommodate divergent system configurations.
For example, conventionally, ASL developers write ACPI code to specify a particular configuration of a platform or its variance. Unfortunately, if even a minor hardware change is performed, the design has to be modified. This requires that new AML code be written and new tables be merged into the system firmware. Thus, the conventional design is not portable or re-usable.
Furthermore, ACPI has conventionally required that a different system firmware ROM (Read Only Memory) or BIOS be used if there is a variance of the platform or if it supports more than one ACPI-aware OS system, where the OS systems have mutually exclusive ACPI requirements. A different system firmware ROM also had to be used if the same system is to support multiple operating systems. For instance current art in personal computers uses the IA-32 instruction set. The Microsoft® family of operating systems primarily used ACPI, especially in systems with the IA-32 instruction set.
ACPI has been accepted by the various operating systems as the standard interface. A new instruction set architecture, IA-64, is being developed, but its advantages cannot be fully utilized with legacy ACPI code, or methods. The new Itanium® Processor Family, available from Intel® Corporation, uses the IA-64 instruction set. The ASL for each new platform or system configuration based on the processor in this family will need to be uniquely rewritten if current practices are utilized.
ACPI namespace is a hierarchical tree structure in OS-controlled memory that contains named objects. These objects may be data objects, control method objects, bus/device package objects, and so on. The OS dynamically changes the contents of the namespace at run-time by loading and/or unloading definition blocks from the ACPI tables that reside in the ACPI BIOS. All the information in the ACPI namespace comes from the differentiated system description table (DSDT), which contains the differentiated definition block, and one or more other definition blocks. In the current art, an OEM (original equipment manufacturer) must supply a DSDT to an ACPI-compatible OS, which supplies the implementation and configuration information about the base system. The OS always inserts the DSDT information into the ACPI Namespace at system boot time and never removes it.
Another ACPI construct is the secondary system description table (SSDT). SSDTs are a continuation of the DSDT. Multiple SSDTs can be used as part of a platform description. After the DSDT is loaded into the ACPI Namespace, each secondary description table with a unique OEM Table ID is loaded. This allows the OEM to provide the base support in one table, while adding smaller system options in other tables. Additional tables can only add data; they cannot overwrite data from previous tables.
A construct in the ACPI architecture defined by the system abstract layer (SAL) is a firmware interface table (FIT). This is an IA-64 instruction set construct. The FIT contains starting addresses and sizes for the firmware components that are outside the protected boot block. A good overview of the FIT entry specification may be found in the “ITANIUM® Processor Family System Abstraction Layer Specification”, Document No. 245359-005, (Intel July 2002), available at http://www.intel.com/design/itanium/downloads/24535905.pdf.